Current induced modifications of domain wall

Abstract

In this paper, current-induced domain wall displacement experiments that are combined with high resolution imaging of the domain walls are reported. A spin-polarized scanning electron microscope is used to determine topography and magnetization distribution of Fe/sub 20/Ni/sub 80/ sub-micron wires with a zigzag geometry. Injection of a single 10 /spl mu/s current pulse through the wire induces the displacement of both head-to-head and tail-to-tail walls in the same direction, which is the direction of the electron flow. The current density of 3 /spl times/10/sup 12/ A/m/sup 2/ is about 10% higher than the threshold current density at which domain wall motion sets in for these structures. This observation confirms unambiguously that the spin-torque effect is the driving force for the domain wall motion. The variation of the domain-wall velocity is correlated with the domain-wall configuration induced by the current. The evolution of domain wall velocities has been determined after consecutive current injections with the same current density. Additional experiments on wires with different dimensions show that the wall velocity depends on the wire width and hence on the domain wall width for constant current density. Simple 1-D models of the domain walls are not sufficient for an adequate description of current-induced domain-wall motion and spin-structure distortion. Thus, the domain walls have to be treated as 2-D objects.